Paul Vallas and others challenging Mayor Rahm Emanuel — and focusing on Chicago’s weak response to the slaughter in the streets — know this about the mayor of Chicago.

He knows how to spin the news.

When he sees criticism coming, Emanuel will offer up some bright, shiny object to change the subject: Like those fanciful Elon Musk sci-fi pneumatic tubes to the airport.

But Chicago’s river of violence overflowed over the weekend, beyond even Emanuel’s capacity to manage the news.

More than 70 people were shot and 12 were killed in weekend shootings, including mass shootings, with few if any arrests. And more have been shot and killed in the days since.

Why don’t people come forward? They’re afraid.

Chicago’s abysmal clearance rates for homicides — about 17 percent last year — can be traced directly to decisions made from City Hall and give the neighborhoods little confidence Emanuel can do much about the bloodshed.

“Emanuel gutted the detective division, now he’s trying to catch up, and the violence in Chicago is out of control,” Vallas told me on Tuesday. “And at some point, you have to put politics aside and you have to manage. The problem is that Emanuel is a D.C. politician, and what do they ever manage in D.C., where every decision made is political? It’s all political, it’s all spin, it’s what they do.”

City Hall calls it “gun violence,” and media cooperates by calling it that, too. But calling it “gun violence” allows Chicago’s political class off the hook.

There are many guns in the suburbs. But the suburbs are not killing grounds. What’s going on in Chicago are street gang wars.

And Cook County’s one-party political class seems incapable of addressing it; from the prosecutors who don’t prosecute, to judges, to the police brass trying to keep their jobs, to Chicago aldermen.

Some aldermen are terrified of the street gangs, which have been intertwined with Chicago politics since the first thugs got out the vote on the first Election Day.

All should be held accountable. But the mayor is most accountable, because he’s the mayor.

When Emanuel walked out before news cameras to react to the crime wave, he demonstrated emotion and outrage. The media likes emotion.

But does emotion carry any real weight with the families of the dead? Does it comfort those who fear their kids will be gunned down tomorrow?

No.

In a city where the street gangs have taken over — where violence carries on through shootings and carjackings even in wealthy neighborhoods like the Gold Coast — talking about feelings just doesn’t cut it anymore.

It’s just noise.

What’s needed is clear policy, which isn’t about emotion, but rather clear thinking.

“Proper policy is about not destroying beat integrity in the Police Department,” Vallas said. “Policy is what I’ve advocated, like rehiring experienced, seasoned detectives to close those murders and give people confidence that something’s being done. But what does Emanuel give the city? Spin.”

At a news conference, Emanuel became emotional and began pointing fingers at others. Standing next to Chicago Police Superintendent Eddie Johnson, the mayor put the focus on his cops and on the neighborhoods for remaining silent.

“This is not about the Chicago Police Department, alone,” Emanuel said. “It’s not about a summer jobs program, alone. This is about the fabric of a neighborhood and community — as the superintendent just said — who knows who did this.

“So, if you say enough is enough, you must come forward as a neighborhood where a moral center of gravity holds,” Emanuel said.

“… If you know who did this, be a neighbor. Speak up. Neighbors, come together. The city will be with you shoulder to shoulder,” Emanuel said.

Emanuel was clearly frustrated and angry. Not everything he does is a political act. He’s a father, he loves his kids, I believe he’s torn up by talking to parents about their murdered children.

But when the mayor declared “the city will be with you,” it stopped me.

The city will be with you? Really?

A 17 percent homicide clearance rate isn’t a declaration that the city will be with you. It says quite the opposite. Years of allowing the Police Department to atrophy doesn’t promote confidence.

And making a show of redeploying cops to high crime areas now is desperation.

What parent would have their child testify against a neighborhood shooter when the city does such a poor job in clearing homicides?

It ignores the real world, where the Police Department went fetal after Emanuel’s disastrous handling of the Laquan McDonald police shooting video.

It ignores the real world of a Police Department allowed to grow so thin that detectives were put back in uniform to serve as scarecrows at lakefront festivals where they can be seen by taxpayers.

All this has little to do with solving homicides.

I mean no criticism of Johnson here. If it weren’t for Johnson, Emanuel would be alone, isolated, political toast. He should have some leverage with a desperate Emanuel.

But Eddie Johnson is not the mayor. Emanuel is the mayor.

The other day there was a telling quote from the Rev. Marshall Hatch, pastor of the New Mount Pilgrim Missionary Baptist Church on the West Side, about why neighbors don’t come forward.

“You put yourself at risk,” Hatch told the Tribune. “Obviously, the police can’t protect you, and if somebody kills you, they can’t find out who did it.”